/Engine/Source/Runtime/SlateCore/Public/Widgets/SWindow.h
Paint the window and all of its contents. Not the same asPaint().
int32 PaintWindow ( double CurrentTime, float DeltaTime, [FSlateWindowElementList](API\Runtime\SlateCore\Rendering\FSlateWindowElementList) & OutDrawElements, const [FWidgetStyle](API\Runtime\SlateCore\Styling\FWidgetStyle) & InWidgetStyle, bool bParentEnabled )